A 3-D imaging system can be used for a product such as a 3-D display TV, or the like, and can be used in order to secure a 3-D imaging for a distant military target, a 3-D imaging for monitoring a natural environment such as a landslide, or the like, and various 3-D imaging around a vehicle required for driving an unmanned autonomous vehicle.
In recent years, a ladar system has gotten the spotlight because high-quality 3-D image is required even under various environments.
A ladar system in the related art, which is used to acquire a 3-D image, includes a panoramic scan ladar (PSL) and a forward looking ladar (FLL). The PSL is disclosed in U.S. patent application publication No. 2011/0216304 (Title: HIGH DEFINITION LIDAR SYSTEM) [hereinafter, referred to as ‘Related Art 1’] and the FLL is disclosed in U.S. Pat. No. 6,414,746 (Title: 3-D IMAGING MULTIPLE TARGET LASER RADAR) [hereinafter, referred to as ‘Related Art 2’′].
Related Art 1 includes a plurality of laser generating modules and a plurality of optical detectors, for example, four laser generating modules and a ‘4×1’ optical detector array. In the case of driving of Related Art 1, the laser generating module and the optical detector array may be configured to operate at different times or at the same time.
However, in Related Art 1, it is difficult to align the respective laser generating modules and respective pairs of optical detectors corresponding thereto so that the plurality of laser generating modules and the optical detector array are scanned in one line form or in a predetermined form. That is, an operation of examining a spatial viewing range of signals detected by the respective optical detectors and modifying a layout of the plurality of laser generating modules and the optical detector array to conform with a specification is required. This process may influence the price of the module and negatively influence mass production.
Further, in Related Art 1, a 2-D image (in general, distance information from a vertical-direction line) can be secured without rotation of the module. In order to acquire the 3-D images, however, an entire transmission/reception module including the plurality of laser modules and the optical detector array may be rotated.
Related Art 2 is constituted by a plurality of optical detectors that irradiates an optical signal generated by a laser generating module to a wide region and thereafter, detects light reflected on and returned from a target, that is, an ‘M×N’ optical detector array. In detail, a pulse laser generating device generating a short pulse evenly irradiates a laser to a wide surface at a predetermined diffusion angle through a diffuser, or the like. In this case, it is characterized that an irradiation region is extended depending on a distance and repeated light pulse irradiation surfaces are generated. The light pulse irradiation surfaces are hit and reflected on the target, reflected optical signals are collected through a light receiving lens, and the collected optical signals are detected through the optical detector array. In this case, the respective detectors of the optical detector array individually operate, measure time differences and magnitudes of the reflected optical signals at every positions of respective pixels, and a 3-D image of an object that reflects the optical signal may be formed by collecting the information.
However, since Related Art 2 requires comparatively high laser pulse power, it is difficult to implement a pulse laser module having a high pulse repetition frequency, and as a result, it is difficult to secure a high frame rate.
Further, In Related Art 2, pixel readout circuits that perform processing such as detecting an optical signal, which is reflected on the object and is incident independently as a pixel signal, are required to detect the signals of the respective optical detectors without influences from neighboring detectors in implementing an optical detector array, the pixel readout circuit parts are arranged in a 2-D array pattern, parts, which transfer and process signals generated from the insides of the pixels, are provided on outer edges thereof, and finally, a readout IC (ROIC), which can transmit the signals to the outside through an interface pad positioned around an edge of a chip, is required.
This type of ROIC includes both digital and analog ROICs. Since a sufficient signal to noise ratio needs to be secured even in a narrow pixel region, it is difficult to implement ROIC and manufacturing cost of the ROIC is high. Further, since the ROIC and the optical detector array are generally implemented by using different substrates, the ROIC and the optical detector array cannot be manufactured at the same time and are connected by a flip-chip method which is comparatively high in terms of cost. Consequently, since a video system having a complicated structure uses a short laser pulse on a wide surface, the video system has a characteristic (flash video) to acquire a still video with respect to an object (for example, rotating wings of a helicopter) which moves at a high speed, and as a result, the video system is used for a military purpose, but in general, total manufacturing cost of the system is high, and as a result, it is difficult to popularize the system.